Researchers are urging medical professionals to stop relying exclusively on the Body-Mass Index to diagnose obesity, according to a major data analysis published in Nature.
The study, released on a Wednesday, examined health records from 844,108 adults across China, the United Kingdom, the United States, and Spain. Investigators discovered that current diagnostic methods frequently fail to distinguish between individuals who face immediate health risks from excess body fat and those who carry extra weight without any measurable organ dysfunction.
“People with obesity deserve care tailored to their needs, no matter less or more,” said Professor Francesco Rubino, senior author of the study and chair of metabolic and bariatric surgery at King’s College London, in a press statement reported by Euronews.com.
The traditional BMI calculation uses only a person’s weight and height. However, it cannot measure actual body fat distribution or determine whether excess tissue has begun harming vital organs.
Flaws in Traditional BMI Screening
The new analysis builds on a framework proposed in January 2025 by a commission in The Lancet Diabetes & Endocrinology. That commission recommended dividing obesity into two distinct categories: clinical obesity, where excess fat disrupts organ function or daily tasks, and preclinical obesity, where health risks rise while normal bodily functions remain intact.
Researchers at King’s College London and international partners wanted to test if this framework predicts health outcomes more accurately than BMI alone.
Their findings revealed that relying strictly on BMI misclassified millions of patients across all four populations.
Alone, the BMI overlooked body fat levels in the obese range for up to 8.6 percent of participants while falsely labeling up to 3.1 percent as obese when they were not. Medscape said that incorporating waist circumference and waist-to-height ratios significantly reduced these diagnostic errors.
Clinical Versus Preclinical Health Risks
The study established that clinical obesity accounted for between 23 percent and 31 percent of all obesity cases, with a total population prevalence ranging from 5.6 percent to 10.9 percent. These two categories point toward vastly different long-term health trajectories. Clinical obesity carried a substantially higher risk of death, whereas preclinical obesity showed only a moderate rise in mortality risk.
Between 77 percent and 91 percent of participants initially categorized with preclinical obesity did not develop clinical obesity over a ten-year observation window. “The Body-Mass Index alone cannot tell us if someone is already sick, has a disease risk, or what care is needed, making people vulnerable to under- and overtreatment,” Rubino told Euronews.com.
Worldwide Implementation Goals
“The clearly different prognoses in clinical and preclinical obesity observed consistently across countries and ethnic groups speak for a worldwide introduction of the new framework,” Pan said, according to Euronews.com.
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